Analysis of the biomechanical properties of the mandible after unilateral distraction osteogenesis

Background: The purpose of this study was to establish biomechanical outcomes measures to evaluate how mandibular distraction osteogenesis affects the overall quality of bone healing. Strength and functional integrity of the regenerate were determined quantitatively after unilateral mandibular distraction osteogenesis in comparison with the contralateral mandible and a partially reduced fracture. The authors hypothesized that the breaking load, yield, and stiffness of mandibular distraction osteogenesis would be significantly reduced in comparison with both the contralateral mandible and a partially reduced fracture. Methods: Sprague-Dawley rats underwent mandibular distraction osteogenesis (n = 8) or a partially reduced fracture (n = 6). Distraction was performed using 4 days' latency and then 0.3 mm every 12 hours for 8 days (5.1 mm). Partially reduced fractures had gaps fixed postoperatively at 2.1 mm. Both groups underwent 4 weeks of consolidation. The contralateral mandibles were used as controls (n = 14). Mandibles were tension tested at 0.5 mm/second to failure, and then breaking load, yield, and stiffness were determined. Results: Mandibular distraction osteogenesis had significantly lower breaking load, yield, and stiffness than contralateral mandible, by 40, 30, and 60 percent, respectively. Breaking load was reduced in partially reduced mandibular fractures by 40 percent when compared with distraction osteogenesis. Conclusions: Using a standard Ilizarov protocol, the biomechanical properties of breaking load, yield, and stiffness in mandibular distraction osteogenesis were significantly lower than those in contralateral mandibles. Surprisingly, the breaking load of mandibular distraction osteogenesis was significantly greater than that of partially reduced mandibular fracture. These verifiable metrics of regenerate integrity can be used to discern optimal outcomes of mandibular distraction osteogenesis, potentially enhancing the clinical applications of this powerful technique.